There seem to be two strands of thought getting mixed up here.

FIrst, should people who have promised to be sexually faithful? A promise is a promise - but if they break it, it is nobody's business but theirs and their lover's/family's.

Second, does it matter whether a politician is sexually unfaithful, gay, indulges in muffin the mule, etc (or even steals excessive expenses). The answer is NO! Politicians are in office to get the best outcome for those they represent (and the philosophy on who they represent varies from system to system).